1. Field of the Invention
This invention relates to a guidewire for facilitating the placement of a catheter within a patient's cardiovascular system. More particularly, the present invention is directed to a flexible, elongate guidewire having enhanced steering properties, that is especially suitable for use in connection with the positioning a balloon dilation catheter in a percutaneous transluminal coronary angioplasty procedure.
2. The Relevant Technology
Catheters are used in a wide variety of medical situations to deliver and administer medicaments to a specific site within a patient's body. Depending on the particular type of medical procedure involved, there is often a need to position a catheter within the patient's body at a specific location, so that a targeted diseased area can then be treated. One example of a medical procedure that requires extremely accurate placement of a catheter is known as percutaneous transluminal coronary angioplasty, or PTCA, which involves the treatment of a narrowed coronary artery caused by a stenosis. In this procedure, a balloon dilation catheter is introduced into the patient's body via a suitable access site, and then advanced through the vasculature until the inflatable portion of the catheter (usually located at the distal end of the catheter) is positioned adjacent to the stenosis that is to be treated. The balloon is then inflated to a predetermined pressure so as to compress the stenosis, and thereby dilate the narrowed vessel.
The nature of a PTCA procedure is such that there is a need to be able to accurately and precisely maneuver the catheter through the patient's vascular system, which typically involves the need to negotiate a series a sharp bends and/or junctions. Typically, this advancement and positioning of the catheter is accomplished with the aid of an elongate, flexible guidewire. The guidewire is first inserted into the patient's vasculature and then the guidewire tip is advanced through the appropriate vessel until it is positioned at a point just beyond the stenosis. The catheter is then advanced over the guidewire to a point where the balloon portion of the catheter is positioned adjacent to the stenosis. Typically, the distal portion of the guidewire is comprised of a radiopaque material such that the advancement and positioning of the guidewire, relative to the stenosis, can be observed by the practitioner fluoroscopically.
Given the nature of the portion of the vascular system typically treated in a PTCA procedure, the PTCA guidewire must be flexible enough so that it can traverse the turns and bends encountered as it is guided to the target vessel. At the same time, the guidewire must be relatively torsionally rigid to allow the guidewire to be manipulated and advanced through the vessel by the practitioner from an external access site. Also, while the distal tip end of the guidewire must be sufficiently flexible so as to be maneuvered through irregular paths, it must be capable of being moved through a partially occluded vessel without kinking or breaking.
The maneuverability and flexibility of a guidewire is often improved by reducing the diameter of the core wire at the distal end. While this improves the flexibility of the distal end of the wire, it also reduces the wire's strength, leaving it susceptible to kinking and/or breaking within the patient's blood vessel. Moreover, depending on the technique used, the reduction in diameter can result in a guidewire having discontinuities in its surface. This can result in trauma to the interior walls of the blood vessel as the guidewire is advanced, and/or may promote the formation of blood clots.
One approach used to address these problems is to wrap a wire spring coil about the distal end of the reduced-diameter portion of the guidewire. The spring coil permits the reduced-diameter portion of the wire to retain its flexibility and at the same time add some structural rigidity to the wire to reduce the risk of breaking and kinking within the blood vessels. However, the approach is not entirely satisfactory in that the outer surface formed by the coil is somewhat irregular and has a relatively higher coefficient of friction than other portions of the guidewire. Again, this can result in trauma to the blood vessel, can result in increased formation of blood clots, and can inhibit the ability to advance the wire through the blood vessel and/or catheter.
As an alternative to using a spring coil, some guidewire designs utilize a plastic coating to completely encase at least a portion of the the tapered distal end of the guidewire's core wire. While such an approach results in a smoother outer surface, the approach also lessens the overall flexibility of the distal end because the plastic, which is stiffer than the wire, completely encases the tapered wire portion. This decrease in flexibility detracts from the overall steerability of the guidewire.
Thus, there is a need for a PTCA guidewire that retains sufficient flexibility in the distal end, and at the same time is not subject to breaking or kinking. Further, the guidewire distal end should have a continuously smooth and uniform outer surface. Finally, the wire should have superior steering characteristics so as to be capable of being maneuvered through the types of blood vessels typically encountered in a PTCA procedure.